Every year, scores of billions of plastic water and soda bottles are purchased and used in the United States alone. Plastic water and soda bottles are often comprised of polyethylene terepthalate (PET), or plastic #1. PET is reported to have a recycling rate of approximately 25 percent; indeed, recycling programs for PET products are relatively ubiquitous. However, nearly every one of those water bottles includes a plastic cap. The caps are typically comprised of polypropylene (PP), or plastic #5. The two plastics cannot generally be recycled together—PP melts at a temperature of nearly 160 degrees Fahrenheit higher than PET. If a cap gets mixed in with bottles, the entire batch may be ruined because there is un-melted plastic in the mix. Therefore, many municipalities do not accept the caps for recycling, or PP products in general.
PP products are, thus, often simply discarded. PP products are not limited to bottle caps. For example, PP products include, for example, common packaging used in containers for cottage cheese, yogurt, cream cheese, ricotta cheese, margarine, hummus, medicine bottles, some plastic ice cream containers, food storage and take-out containers, as well as flip caps on tubes and food product bottles (e.g., condiments), jar lids (e.g., peanut butter), and laundry detergent lids. At best, when not recycled, these PP products end up in landfills. Too often, PP products such as bottle caps end up as litter, where they pose a significant hazard to wildlife and the environment.
Not only do discarded PP products present an environmental risk, but they also represent lost opportunity. Polypropylene is a hydrocarbon, as are gaseous and liquid fuels and oils. Proper decomposition of PP products should yield useful hydrocarbon products. Thus, methods and systems are needed to decompose waste PP products into useful hydrocarbon products, including fuels.